The present invention relates to microlenses, and more particularly to liquid microlenses.
Most tunable microlenses are either gradient index (GRIN) lenses with the refractive index controlled electrostatically or flexible polymeric lenses with the shape controlled mechanically. Both technologies have inherent limitations that impose severe restrictions on the performance of these existing tunable microlenses.
Tunable gradient index lenses have inherent limitations associated with the relatively small electro-optic coefficients found in the majority of electro-optic materials. This results in a small optical path modulation and, therefore, requires thick lenses or very high voltages to be employed. In addition, many electro-optic materials show a strong birefringence that causes polarization dependence of the microlens properties.
Mechanically adjustable flexible lenses typically have a substantially wider range of tunability than the gradient index lenses. However, they require external actuation devices, such as micropumps, to operate. Microintegration of such devices involves substantial problems, especially severe in the case where a two-dimensional array of tunable microlenses is required.
Attempts have also been made to use other technologies to produce tunable microlenses, such as liquid microlenses controlled by absorption and desorption of self-assembled monolayers (SAMs). Some of these attempts are described in U.S. Pat. No. 6,014,259 to Wohlstadter, issued Jan. 11, 2000, the entirety of which is hereby incorporated by reference herein. Microlenses utilizing absorption and desorption of self-assembled monolayers, however, also suffer from several problems, including severe limitations on material selection and strong hysteresis leading to the failure of the microlens to return to an original shape after a tuning voltage is disconnected. Additionally, none of the above-described microlenses allow for both lens position adjustment and focal length tuning.
A tunable liquid microlense that utilizes electrowetting-based tuning is described in Applicants"" copending applicationsxe2x80x94U.S. patent application Ser. No. 09/884,605, filed Jun. 19, 2001, entitled xe2x80x9cTunable Liquid Microlensxe2x80x9d and U.S. patent application Ser. No. 09/951,637, filed Sep. 13, 2001, entitled xe2x80x9cTunable Liquid Microlens With Lubrication Assisted Electrowetting.xe2x80x9d The tunable liquid microlense allows for both lens position adjustment and focal length tuning.
We have recognized that while the ""605 and ""637 applications provide exemplary electrowetting-based tunable liquid microlenses, there remains a need to provide a tunable liquid microlens that does not rely on electrowetting in order to tune the microlens. In particular, in certain applications it may be advantageous to have a microlens that can be tuned using irradiation by light. Such a microlens would allow for additional functionality when compared to an electrowetting controlled microlens. For example, self alignment of the microlens with the collimated light beam or a direct control of the microlens properties by the light beam intensity and/or wavelength may be achieved.
Therefore, we have developed in accordance with the principles of the invention a liquid microlens that is photo-tunable, i.e., responsive to a light source. Such a photo-tunable liquid microlens includes a transparent supporting layer and a transparent photoresponsive layer disposed on a first surface of the supporting layer. A droplet of a transparent liquid is disposed on the photoresponsive layer. The photoresponsive layer separates the supporting layer and the droplet. In accordance with an aspect of the invention, at least a portion of the photoresponsive layer that contacts the droplet may be selectively irradiated by at least one light source such that a contact angle between the droplet and the photoresponsive layer may be varied and the droplet may be repositioned along the photoresponsive layer. In this manner, at least one of a focal length and a lateral position of a focal spot of the microlens may be adjusted. Note that by xe2x80x9clight,xe2x80x9d it is meant electromagnetic radiation, including, but not limited to, X-Rays, ultraviolet, visible, infrared, radiowave, and radar sources.
The photo-tunable liquid microlens allows for both lens position and focal length tuning. In addition, the ability to respond to light allows for (a) a self alignment of the microlens with a collimated light beam or (b) a direct control of the microlens properties by varying the light beam intensity and/or wavelength.